Integrated circuits

ABSTRACT

An integrated circuit includes a gate electrode disposed over a substrate. A source/drain (S/D) region is disposed adjacent to the gate electrode. The S/D region includes a diffusion barrier structure disposed in a recess of the substrate. The diffusion barrier structure includes a first portion and a second portion. The first portion is adjacent to the gate electrode. The second portion is distant from the gate electrode. An N-type doped silicon-containing structure is disposed over the diffusion barrier structure. The first portion of the diffusion barrier structure is configured to partially prevent N-type dopants of the N-type doped silicon-containing structure from diffusing into the substrate. The second portion of the diffusion barrier structure is configured to substantially completely prevent N-type dopants of the N-type doped silicon-containing structure from diffusing into the substrate.

TECHNICAL FIELD

The present disclosure relates generally to the field of semiconductor devices and, more particularly, to integrated circuits and methods of forming the integrated circuits.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. However, these advances have increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed.

In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling-down also produces a relatively high power dissipation value, which may be addressed by using low power dissipation devices such as complementary metal-oxide-semiconductor (CMOS) devices.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale and are used for illustration purposes only. In fact, the numbers and dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1A is a schematic cross-sectional view of an exemplary integrated circuit.

FIGS. 1B-1D are various magnified schematic cross-sectional views of a S/D region of an exemplary integrated circuit.

FIG. 2 is a flowchart of an exemplary method of forming an integrated circuit.

FIGS. 3A-3F are schematic cross-sectional views of an integrated circuit during various fabrication stages.

FIG. 4A is schematic drawing illustrating a thermal profile of an anneal process.

FIG. 4B is schematic drawing illustrating a thermal profile of another anneal process.

FIG. 4C is a magnified schematic drawing of an exemplary spike anneal of the anneal process shown in FIG. 4B.

FIG. 5 is a schematic drawing showing secondary ion mass microscopy (SIMS) profiles S/D regions of integrated circuits processed by different conditions

DETAILED DESCRIPTION

Generally, a plurality of ion implantations have been implemented for forming source/drain (S/D) regions, lightly-doped drain (LDD) regions, and pocket regions of transistors. For example, an N-type source/drain (NSD) process has a room-temperature phosphorus ion implantation that is provided to form a gradient dopant junction profile in a substrate. A room-temperature carbon ion implantation is then performed to the S/D regions to prevent over diffusion of phosphorus dopants into the substrate. A room-temperature arsenic ion implantation and a room-temperature phosphorus ion implantation are performed to form S/D doped regions. After the multiple ion implantations, a rapid thermal anneal (RTA) is performed to active dopants and cure damage resulting from the ion implantations. Silicide is then formed at the top of the S/D doped regions.

As noted, the process described above uses the room-temperature phosphorus ion implantation to form the junction profile. When transistors are scaled down, the S/D junction profile may be too deep. The multiple ion implantations may also substantially damage the S/D regions. To cure the damage, a high thermal budget, e.g., a higher RTA temperature of about 1050° C. and/or a longer RTA time, may be applied. The high thermal budget may aggravate a short-channel effect (SCE) within the transistors. If a low thermal budget is applied, implantation damage may not be desirably cured. The low thermal budget may also result in transient-enhanced diffusion (TED).

It is understood that the following descriptions provide many different embodiments, or examples, for implementing different features of the disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Moreover, the formation of a feature on, connected to, and/or coupled to another feature in the present disclosure that follows may include embodiments in which the features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the features, such that the features may not be in direct contact. In addition, spatially relative terms, for example, “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top,” “bottom,” etc. as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) are used for ease of the present disclosure of one feature's relationship to another feature. The spatially relative terms are intended to cover different orientations of the device including the features.

FIG. 1A is a schematic cross-sectional view of an exemplary integrated circuit. In FIG. 1A, an integrated circuit 100 includes a gate electrode 103 that is disposed over a substrate 101. Source/drain regions 107 a and 107 b are adjacent to the gate electrode 103. In some embodiments, the integrated circuit 100 can be a digital circuit, an analog circuit, a mixed-signal circuit, a static random access memory (SRAM) circuit, an embedded SRAM circuit, dynamic random access memory (DRAM) circuit, an embedded DRAM circuit, a non-volatile memory circuit, e.g., FLASH, EPROM, E²PROME, a field-programmable gate circuit, or any combinations thereof.

In some embodiments forming an N-type transistor, the substrate 101 can be a silicon substrate doped with P-type dopants, such as boron (a P-type substrate). In other embodiments, the substrate 101 may alternatively be made of some other suitable elementary semiconductor, such as diamond or germanium; a suitable compound semiconductor, such as silicon carbide, silicon germanium, indium arsenide, or indium phosphide; or a suitable alloy semiconductor, such as silicon germanium carbide, gallium arsenic phosphide, or gallium indium phosphide. Further, the substrate 101 could include an epitaxial layer (epi layer), may be strained for performance enhancement, and may include a silicon-on-insulator (SOI) structure.

In some embodiments, the gate electrode 103 can be a conductive gate structure, e.g., a polysilicon gate structure, a metal gate structure, a dummy gate structure, or any suitable gate structure. For example, a conductive gate structure can have a stack structure including a gate dielectric layer, a conductive material layer, and/or other suitable layers. A metal gate structure can have a stack structure including a high dielectric constant gate layer, a diffusion barrier layer, a metal work function layer, a metallic layer, and/or other suitable layers. A dummy gate structure can have a stack structure including a dummy material layer, a hard mask layer, and/or other suitable layers.

Referring to FIG. 1A, spacers 105 a and 105 b are each disposed on respective sidewalls of the gate electrode 103. In some embodiments, the spacers 105 a and 105 b can be made of at least one material, such as silicon oxide, silicon nitride, silicon oxynitride, silicon carbide, silicon oxycarbide, silicon carbon nitride, other dielectric materials, and/or any combinations thereof.

Referring again to FIG. 1A, diffusion barrier structures 111 a and 111 b are disposed in recesses 120 a and 120 b of the substrate 101, respectively. N-type doped silicon-containing structures 130 a and 130 b are disposed over the diffusion barrier structures 111 a and 111 b, respectively. In some embodiments, the dopants concentration of the N-type doped silicon-containing structures 130 a and 130 b may range from about 2E20 cm⁻³ to about 1E21 cm⁻³.

Referring to FIG. 1A, the diffusion barrier structures 111 a and 111 b are configured to prevent N-type dopants, e.g., phosphorus, of the N-type doped silicon-containing structures 130 a and 130 b, respectively, from diffusing into the substrate 101. By controlling the diffusion of N-type dopants of the N-type doped silicon-containing structures 130 a and 130 b, the short channel effect of the transistor of the integrated circuit 100 can be reduced.

Referring to FIG. 1A, the diffusion barrier structures 111 a and 111 b include epitaxial carbon-containing layers 125 a and 125 b, respectively. In some embodiments, the epitaxial carbon-containing layers 125 a and 125 b can each have a carbon dopant concentration of about 0.1 atomic percent to about 1 atomic percent. In some embodiments, the epitaxial carbon-containing layers 125 a and 125 b can be made of at least one material, such as silicon carbide (SiC), silicon oxycarbide (SiOC), silicon carbon nitride (SiCN), silicon carbon phosphorus (SiCP), other carbon-containing materials, and/or any combinations thereof. With the carbon dopants, the epitaxial carbon-containing layers 125 a and 125 b can partially and/or completely reduce the diffusion of the N-type dopants of the N-type doped silicon-containing structures 130 a and 130 b into the substrate 101.

In some embodiments, the integrated circuit 100 optionally includes lightly-doped drains (LDDs) 109 a and 109 b. For the embodiments forming an N-type transistor, the LDDs 109 a and 109 b include n-type dopants, e.g., phosphorus and/or arsenic. The LDDs 109 a and 109 b are configured to reduce the resistance between the S/D regions 107 a and 107 b. In some embodiments, the LDDs 109 a and 109 b may enhance the short channel effect, if the channel length between the S/D regions 107 a and 107 b is shrunk to the order of nanometer.

Referring to FIG. 1A, the diffusion barrier structure 111 a and 111 b may optionally comprise carbon implanted regions 108 a and 108 b between the epitaxial carbon-containing layer 125 a and 125 b and the substrate 101, respectively. The carbon implanted regions 108 a and 108 b can reduce the diffusion of n-type dopants from the LDDs 109 a and 109 b into the channel of the transistor, such that the short channel effect can be reduced. In some embodiments, the carbon implanted regions 108 a and 108 b can have a carbon dopants concentration ranging from about 0.1 atomic percent to about 1 atomic percent.

It is noted that though showing both of the LDDs 109 a-109 b and the carbon implanted regions 108 a-108 b in FIG. 1A, the scope of this application is not limited thereto. In some embodiments, the carbon implanted regions 108 a-108 b are formed in the substrate 101, whereas the LDDs 109 a-109 b are skipped if the short channel effect outweighs the resistance between the S/D regions 107 a and 107 b. In other embodiments, the LDDs 109 a-109 b are formed in the substrate 101, whereas the carbon implanted regions 108 a-108 b are skipped, if the resistance outweighs the short channel effect.

FIG. 1B is an exemplary magnified schematic cross-sectional view of the S/D region 107 b of the integrated circuit 100. In FIG. 1B, the diffusion barrier structure 111 b includes portions 112 a and 112 b. The portion 112 a is adjacent to the gate electrode 103 and close to the channel under the gate electrode 103. In contrast to the portion 112 a, the portion 112 b is distant from the gate electrode 103. The portion 112 a of the diffusion barrier structure 111 b is configured to partially prevent N-type dopants of the N-type doped silicon-containing structure 130 b from diffusing into the substrate 101, e.g., the channel under the gate electrode 103. The partial diffusion of the N-type dopants of the N-type doped silicon-containing structure 130 b into the channel reduces the resistance between the S/D regions 107 a and 107 b. The portion 112 b of the diffusion barrier structure 111 b is configured to substantially completely prevent N-type dopants of the N-type doped silicon-containing structure 130 b from diffusing into the substrate 101.

In some embodiments to achieve different diffusion blocking effects in different regions, the epitaxial carbon-containing layers 125 b of the diffusion barrier structure 111 b includes regions 127 a-127 c. The region 127 a is adjacent to the gate electrode 103 and the region 127 c is distant from the gate electrode 103. As shown in FIG. 1B, the regions 127 a and 127 c have thicknesses T₁ and T₂, respectively. The thickness T₁ is smaller than the thickness T₂. In some embodiments, the thickness T₁ can range from about 2 nm to about 5 nm. The thickness T₂ can range from about 5 nm to about 15 nm. It is noted that the thickness ranges of the regions 127 a and 127 c are merely exemplary. In some embodiments, the thickness ranges may vary in response to the change of the technology node.

As noted, the region 127 a is thinner than the region 127 c. Due the thickness difference, the N-type dopants of the N-type doped silicon-containing structure 130 b are partially blocked by the region 127 a and substantially completely blocked by the region 127 c. With the partial diffusion of the N-type dopants of the N-type doped silicon-containing structure 130 b into the channel, the resistance between the S/D regions 107 a and 107 b is reduced. Also, because of the partial blocking of the N-type dopants of the N-type doped silicon-containing structure 130 b into the channel, the short channel effect is controlled.

Referring to FIG. 1B, an interface 129 a between the region 127 a of the epitaxial carbon-containing layer 125 b and the substrate 101 is directly under the gate electrode 103. In some embodiments, the interface 129 a is misaligned from a sidewall 103 a of the gate electrode 103 by a distance W. In some embodiments, the distance W is about 2 nm or less. It is noted that the distance W described above is merely exemplary. The scope of this application is not limited thereto. In some embodiments, the distance W may be larger depending on the change of the technology node.

As noted, the recess 120 b may entrench under the gate electrode 103. The sidewall 121 b of the recess 120 b is directly under the gate electrode 103. The encroachment of the recess 120 b under the gate electrode 103 may allow the N-type doped silicon-containing structure 130 b to be formed close to the channel under the gate electrode 103. The closure of the N-type doped silicon-containing structure 130 b to the channel reduces the resistance between the S/D regions 107 a and 107 b.

In other embodiments, an interface 129 a′ between the region 127 a of the epitaxial carbon-containing layer 125 b and the substrate 101 is not directly under the gate electrode 103 as shown in FIG. 1C. The sidewall 121 b′ of the recess 120 b is not directly under the gate electrode 103. In some embodiments, the interface 129 a′ is misaligned from the sidewall 103 a of the gate electrode 103 by a distance W′. In some embodiments, the distance W′ is about 10 nm or less. It is noted that the distance W′ described above is merely exemplary. The scope of this application is not limited thereto. In some embodiments, the distance W′ may be larger depending on the change of the technology node.

As shown in FIG. 1C, the distance W′ may keep the N-type doped silicon-containing structure 130 b from the channel under the gate electrode 103. Compared with the structure shown in FIG. 1B, the remoteness of the N-type doped silicon-containing structure 130 b to the channel may reduce the short channel effect.

Referring again to FIG. 1B, in some embodiments the region 127 a of the epitaxial carbon-containing layer 125 b continuously extends from a surface 101 a of the substrate 101 along the sidewall 121 b of the recess 120 b for a depth D. In some embodiments, the depth D is about 7 nm or less. The region 127 a may be substantially orthogonal to the surface 101 a of the substrate 101. In other embodiments, the region 127 a may tilt an angle with respect to the surface 101 a and toward the region 127 c.

In some embodiments, the region 127 a has a substantially conformal thickness along the sidewall 121 b of the recess 120 b as shown in FIG. 1B. In other embodiments, the thickness of the region 127 a′ gradually increases from the surface 101 a of the substrate and along the sidewall of the recess 120 b as shown in FIG. 1D. In FIG. 1D, the thickness T₁′ of the region 127 a′ is calibrated at the middle of the region 127 a′.

Following are descriptions of forming an exemplary integrated circuit. Illustrated in FIG. 2 is a flowchart of an exemplary method of forming an integrated circuit. FIGS. 3A-3F are schematic cross-sectional views of an integrated circuit during various fabrication stages. Items of FIGS. 3A-3F that are the same or similar items in FIG. 1A are indicated by the same reference numerals, increased by 200. It is understood that FIGS. 2 and 3A-3F have been simplified for a better understanding of the concepts of the present disclosure. Accordingly, it should be noted that additional processes may be provided before, during, and after the methods described in conjunction with FIGS. 2 and/or 3A-3F, and that some other processes may only be briefly described herein.

Referring now to FIG. 2, a method 200 of forming an integrated circuit includes forming a gate electrode over a substrate (block 210). A recess is formed in the substrate and adjacent to the gate electrode (block 220). A diffusion barrier structure is formed in the recess (block 230). The diffusion barrier structure includes a first portion and a second portion, the first portion is adjacent to the gate electrode, and the second portion is distant from the gate electrode. An N-type doped silicon-containing structure is formed over the diffusion barrier structure (block 240). The first portion of the diffusion barrier structure is configured to partially prevent N-type dopants of the N-type doped silicon-containing structure from diffusing into the substrate and the second portion of the diffusion barrier structure is configured to substantially completely prevent N-type dopants of the N-type doped silicon-containing structure from diffusing into the substrate. The method 200 includes thermally annealing the N-type doped silicon-containing structure (block 250).

Referring to FIG. 2, a gate electrode is formed over a substrate (block 210). For example, a gate electrode 303 can be formed over the substrate 301 as shown in FIG. 3A. Spacers 305 a and 305 b are formed on sidewalls of the gate electrode 303. S/D regions 307 a and 307 b are disposed adjacent to the sidewalls of the gate electrode 303.

In some embodiments, an implantation process 310 can implant carbon dopants into the substrate 301, forming carbon implanted regions 308 a and 308 b. In some embodiments, the implantation process 310 can have an implantation energy ranging from about 1 KeV to about 5 KeV, an implantation dosage ranging from about 5E14 cm⁻² to about 2E15 cm⁻², and an implantation tilt angle with respect to a direction orthogonal to the surface 301 a of the substrate ranging from about 0° to about 25°. It is noted that the formation of the carbon implanted regions 308 a and 308 b is optional. The carbon implanted regions 308 a and 308 b are portions of diffusion barrier structures that will be described below.

In some embodiments using a gate-first process, the gate electrode 303 can include a polysilicon gate structure or a metal gate structure. For example, a conductive gate structure can have a stack structure including a gate dielectric layer, a conductive material layer, and/or other suitable layers. A metal gate structure can have a stack structure including a high dielectric constant gate layer, a diffusion barrier layer, a metal work function layer, a metallic layer, and/or other suitable layers.

In other embodiments using a gate-last process, the gate electrode 303 can include a dummy gate structure. The dummy gate structure can have a stack structure including a dummy material layer, a hard mask layer, and/or other suitable layers. The dummy gate structure will be removed after the formation of the S/D structures in the S/D regions 307 a and 307 b.

In some embodiments, another implantation process 315 can be optionally utilized to form lightly-doped drains (LDDs) 309 a and 309 b in the substrate 301 as shown in FIG. 3B. In some embodiments, portions of the LDDs 309 a and 309 b can be formed directly under the gate electrode 303. In other embodiments, the LDDs 309 a and 309 b are not covered by the gate electrode 303. The LDDs 309 a and 309 b can be formed of n-type dopants (impurities). For example, the dopants can comprise phosphorous, arsenic, and/or other group V elements. In some embodiments, at least one thermal annealing process, e.g., a rapid thermal annealing (RTA) process, can be performed to activate the dopants of the LDDs 309 a and 309 b. In some embodiments, the RTA process can have a spike annealing temperature of about 950° C.

Referring to FIG. 2, a recess is formed in the substrate and adjacent to the gate electrode (block 220). For example, an etch process 319 removes portions of the substrate 301, forming recesses 320 a and 320 b in the substrate 301 as shown in FIG. 3C. The etch process 319 can include an isotropic etch process, an anisotropic etch process, and/or any combinations thereof.

In some embodiments using an isotropic etch process, the profiles of the recesses 320 a and 320 b can be achieved as shown in FIG. 3C. The magnified profiles of the recesses 320 a and 320 b can be the same as or similar to those described above in conjunction with FIGS. 1B-1D. In some embodiments, the sidewall 321 b of the recess 320 b can be the same as or similar to the sidewall 121 b of the recess 120 b describe above in conjunction with FIG. 1B. In at least this embodiment, the sidewall 321 b of the recess 320 b is directly under the gate electrode 303 and misaligned from a sidewall 303 a of the gate electrode 303 by about 2 nm or less. In other embodiments, the sidewall 321 b of the recess 320 b can be the same as or similar to the sidewall 121 b′ of the recess 120 b describe above in conjunction with FIG. 1C. In at least this embodiment, the sidewall 321 b of the recess 320 b is not directly under the gate electrode 303 and misaligned from a sidewall 303 a of the gate electrode 303 by about 10 nm or less.

In other embodiments using an anisotropic etch process, the sidewall 321 b of the recess 320 b can be substantially orthogonal to the surface 301 a of the substrate 301. As the sidewall 321 b is used as an etch mask of the etch process 319, the sidewall 321 b can be substantially aligned with the spacer 305 b.

Referring again to FIG. 2, a diffusion barrier structure is formed in the recess (block 230). In some embodiments, the formation of the diffusion barrier structure includes epitaxially forming a carbon-containing layer in the recess. For example, carbon-containing layers 325 a and 325 b are epitaxially formed in the recesses 320 a and 320 b, respectively, as shown in FIG. 3D. The carbon-containing layers 325 a and 325 b each have a carbon concentration of about 0.1 atomic percent (%) to about 1 atomic percent. In some embodiments, the profile of the carbon-containing layers 325 a and 325 b can be the same as or similar to those described above in conjunction with FIGS. 1B-1D. For example, the diffusion barrier structure 111 b includes portions 112 a and 112 b as described above in conjunction with FIG. 1B. The portion 112 a is adjacent to the gate electrode 103 and the portion 112 b is distant from the gate electrode 103.

In some embodiments, the carbon implanted regions 308 a, 308 b and the respective carbon-containing layers 325 a, 325 b can be referred to as diffusion barrier structures 311 a and 311 b, respectively. As noted, the carbon implanted regions 308 a and 308 b are optional. In other embodiments, the diffusion barrier structures 311 a and 311 b each only includes the respective carbon-containing layers 325 a and 325 b.

Referring to FIG. 2, an N-type doped silicon-containing structure is formed over the diffusion barrier structure (block 240). For example, N-type doped silicon-containing structures 330 a and 330 b are formed over the diffusion barrier structures 311 a and 311 b, respectively, as shown in FIG. 3E. The N-type doped silicon-containing structures 330 a and 330 b are referred to as heavily doped S/D regions. In some embodiments, the N-type doped silicon-containing structures 330 a and 330 b are epitaxially formed over the diffusion barrier structures 311 a and 311 b. The formation of the N-type doped silicon-containing structures 330 a and 330 b can utilize a cyclic deposition etch (CDE) process, a selective epitaxial growth (SEG) process, and/or any combinations thereof.

Applicants find that an implantation/anneal process for forming heavily doped S/D regions may activate dopants concentration up to about 2E20 cm⁻³. Due to the restriction, the resistance at the heavily doped S/D regions may not be further reduced. Different from the implantation/anneal process, the N-type doped silicon-containing structures 330 a and 330 b are formed by an epitaxial process. N-type dopants can be in-situ doped during the epitaxial process and a higher dopant concentration can be achieved. In some embodiments, the N-type doped silicon-containing structure 330 a and 330 b each have a dopant concentration ranging from about 2E20 cm⁻³ to about 1E21 cm⁻³. By increasing the dopant concentration, the resistances of the N-type doped silicon-containing structure 330 a and 330 b are reduced. The “on” current of the transistor following through the N-type doped silicon-containing structure 330 a and 330 b is enhanced. In some embodiments, epitaxially forming the N-type doped silicon-containing structures 330 a and 330 b can be referred to as a concentration enhanced diffusion.

Applicants also find that the high dopant concentration of the N-type doped silicon-containing structure 330 a and 330 b may also aggravate the short channel effect due to dopant diffusion into the channel under the gate electrode 303. As noted, the diffusion barrier structures 311 a and 311 b are configured to partially and/or completely prevent dopant diffusion from the N-type doped silicon-containing structures 330 a and 330 b depending on the regions. The dopant diffusion blocking can reduce the short channel effect.

In some embodiments, the N-type doped silicon-containing structure 330 b includes portions 312 a and 312 b as shown in FIG. 3E. The portion 312 a is adjacent to the gate electrode 303 and the portion 312 b is distant from the gate electrode 312 b. The portion 312 b of the diffusion barrier structure 325 b is configured to substantially completely prevent N-type dopants of the N-type doped silicon-containing structure 330 b from diffusing into the substrate 301. The portion 312 a of the diffusion barrier structure 325 b is configured to partially prevent N-type dopants of the N-type doped silicon-containing structure 330 b from diffusing into the substrate 301. The partial diffusion of the N-type dopants through the diffusion barrier structure 325 b reduces the resistance between the S/D regions 307 a and 307 b, while the short channel effect is controlled.

Referring again to FIG. 2, the method 200 includes thermally annealing the N-type doped silicon-containing region (block 250). For example, after the formation of the N-type doped silicon-containing structures 330 a and 330 b, a thermal process 335 is performed to activate N-type dopants of the N-type doped silicon-containing structures 330 a and 330 b as shown in FIG. 3F. Due to the high dopant concentration of the N-type doped silicon-containing structures 330 a and 330 b, the thermal process 335 is controlled such that the thermal budget does not substantially affect the dopant profile of the N-type doped silicon-containing structures 330 a and 330 b. The N-type dopants of the N-type doped silicon-containing structures 330 a and 330 b do not substantially diffuse into the channel under the gate electrode 303 and does not aggravate the short channel effect.

In some embodiments, the thermal process 335 may use a single or multiple preheat stages. Following the single or multiple preheat stages, a spike anneal is performed to activate the dopants of the N-type doped silicon-containing structures 330 a and 330 b.

In some embodiments, the thermal process 335 uses a single preheat stage having a temperature ranging from about 550° C. to about 700° C. with a duration in a range from about 5 seconds to about 10 seconds. In other embodiments, the thermal process 335 uses multiple preheat stages, e.g., two preheat stages. In addition to the first preheat stage described above, a second preheat stage is performed to warm up the substrate. The second preheat stage can have a temperature ranging from about 500° C. to about 600° C. with a duration in a range from about 5 seconds to about 10 seconds. In some embodiments, the multiple preheat stages can be illustrated by a thermal profile including temperatures T₁, T₂ and durations t₁, t₂ as shown in FIG. 4A.

After the single or multiple preheat stages, the thermal process 335 includes a spike anneal stage. In some embodiments, the spike anneal stage can have an anneal spike temperature T_(Peak) ranging from 875° C. to 990° C. The spike anneal stage can be performed with a temperature T_(Peak-50C) ranging from 825° C. to 940° C. for a time duration t_(peak-50C) in a range from about 0.7 seconds to about 2.4 seconds. The temperature T_(Peak-50C) means that the temperature is below a peak temperature T_(Peak) by about 50° C. as shown in FIG. 4A. The time duration t_(Peak-50C) means the anneal time during the thermal process at temperature T_(Peak-50C). As the spike anneal stage is performed for a timeframe on the order of the second level, the thermal process 335 described above in conjunction with FIG. 4A, in some embodiments, can be referred to as a rapid thermal process (RTP) spike anneal process.

In other embodiments, the spike anneal stage can be performed for a timeframe on the order of the millisecond level. For example, the thermal process 335 includes multiple preheat stages, e.g., two preheat stages as shown in FIG. 4B. In some embodiments, the first preheat stage has a temperature T₁′ in a range from about 500° C. to about 800° C. with a duration t₁′ in a range from about 2 seconds to about 20 seconds. The second preheat stage has a temperature T₂′ in a range from about 500° C. to about 800° C. with a duration t₂′ in a range from about 2 seconds to about 20 seconds. After the second preheat stage, the anneal temperature is quickly raised to the peak anneal temperature T_(Peak)′ by millisecond anneal. The quick rise of the anneal temperature can be referred to as the spike anneal stage. In some embodiments, the spike anneal stage is referred to as a flash anneal. The spike anneal has the peak anneal temperature T_(Peak)′ ranging from about 1,000° C. to about 1,100° C. with a duration in a range from about 0.8 milliseconds to about 15 milliseconds. For example, FIG. 4C is a magnified drawing of the spike anneal shown in FIG. 4B. In FIG. 4C, the spike anneal stage includes one of temperature profiles of multiple millisecond anneal times (or soak times) from 2 ms, 3 ms, 5 ms, 7 ms and 9 ms.

It is noted if a conventional RTA process were applied to the structure shown in FIG. 3F, the dopants of the N-type doped silicon-containing structures 330 a and 330 b would have diffused into the channel under the gate electrode 303 and/or the substrate 301. The post-RTA dopant profile tails and is not parallel to the as-deposited dopant profile of the N-type doped silicon-containing structures 330 a and 330 b. The tail of the dopant profile devastates the short channel effect.

Contrary to the conventional RTA process, the thermal process 335 has the single or multiple preheat stages and a short duration spike anneal stage. The low thermal budget of the thermal process 335 substantially reduces the diffusion of the dopants of the N-type doped silicon-containing structures 330 a and 330 b into the channel under the gate electrode 303 and/or the substrate 301.

For example, FIG. 5 is a schematic drawing showing secondary ion mass microscopy (SIMS) profiles S/D regions of integrated circuits processed by different conditions. In FIG. 5, samples A-E are prepared by the methods described above in conjunction with FIGS. 2 and 3A-3F. Samples A-E have the same thickness, e.g., about 30 nm, of the epitaxial N-type doped silicon-containing structures 330 a and 330 b, but have different carbon concentrations and thicknesses of carbon-containing layers 325 a and 325 b, and different thermal processes 335.

Referring to FIG. 5, sample A includes the epitaxial N-type doped silicon-containing structures 330 a and 330 b not subjected to the thermal process 335. Sample A has the carbon-containing layers 325 a and 325 b having a thickness of about 2 nm and carbon concentration of about 0.7%.

Samples B-D have the structures that are the same as Sample A. Samples B-D are subjected to different thermal processes. Sample B is subjected to two preheat stages and a second level spike anneal stage at a temperature of about 900° C. Sample C is subjected to two preheat stages and a second level spike anneal stage at a temperature of about 950° C. Sample D is subjected to a single preheat stage at a temperature of about 800° C. and a millisecond level spike anneal stage at a temperature of about 1050° C.

Sample E has the carbon-containing layers 325 a and 325 b having a thickness of about 3 nm and carbon concentration of about 0.3%. Sample E is then subjected to a single preheat stage at a temperature of about 800° C. and a millisecond level spike anneal stage at a temperature of about 1050° C.

As shown in FIG. 5, after different thermal processes the SIMS profiles of samples B-E are parallel-shifted with respect to the SIMS profile of sample A by a small distance. The parallel shift means the thermal budgets of the thermal processes applied to samples B-E substantially reduce the dopant diffusion from the N-type doped silicon-containing structures 330 a and 330 b. Though the SIMS profiles of samples B-E tail below the dopant concentration 1E18 cm⁻³, the tails of the dopant profiles do not substantially affect the short channel effect.

As noted, the method 200 described above in conjunction with FIG. 2 can be a gate-last process. In some embodiments using the gate-last process, the method 200 can include a gate replacing process. The gate electrode 303 is a dummy gate structure. The dummy gate structure includes a hard mask material formed over a dummy gate material. The dummy gate material can be made of at least one material such as polysilicon, amorphous silicon, silicon oxide, silicon nitride, or a material having an etching rate that is substantially different from the spacers.

After the formation of the N-type doped silicon-containing structures 330 a and 330 b described above in conjunction with FIG. 3F, the hard mask materials and the dummy gate materials can be removed, for example, by a wet etch process, a dry etch process, or any combinations thereof. After removing the dummy gate materials, the gate-last process can include forming gate electrode material within openings in which the dummy gate materials are disposed. In some embodiments, the gate electrode material can be a stack structure including a diffusion barrier layer, a metallic work function layer, a metallic conductive layer, and/or other suitable material layers.

In some embodiments, at least one high dielectric constant (high-k) layer (not shown) can be formed under the gate electrode material. The high-k dielectric layer can include high-k dielectric materials such as HfO₂, HfSiO, HfSiON, HfTaO, HfTiO, HfZrO, other suitable high-k dielectric materials, or any combinations thereof. In some embodiments, the high-k material may further be selected from metal oxides, metal nitrides, metal silicates, transition metal-oxides, transition metal-nitrides, transition metal-silicates, oxynitrides of metals, metal aluminates, zirconium silicate, zirconium aluminate, silicon oxide, silicon nitride, silicon oxynitride, zirconium oxide, titanium oxide, aluminum oxide, hafnium dioxide-alumina alloy, other suitable materials, or any combinations thereof.

In some embodiments, the diffusion barrier can be configured to prevent metallic ions of the work function metal material from diffusing into the gate dielectric material. The diffusion barrier may comprise at least one material such as aluminum oxide, aluminum, aluminum nitride, titanium, titanium nitride (TiN), tantalum, tantalum nitride, other suitable material, and/or combinations thereof.

In some embodiments, the metallic work function layer can include at least one P-metal work function layer and/or at least one N-metal work function layer. The P-type work function materials can include compositions such as ruthenium, palladium, platinum, cobalt, nickel, and conductive metal oxides, and/or other suitable materials. The N-type metal materials can include compositions such as hafnium, zirconium, titanium, tantalum, aluminum, metal carbides (e.g., hafnium carbide, zirconium carbide, titanium carbide, aluminum carbide), aluminides, and/or other suitable materials. In some embodiments, the metallic conductive layer can be made of at least one material, such as aluminum, copper, Ti, TiN, TaN, Ta, TaC, TaSiN, W, WN, MoN, MoON, RuO₂, and/or other suitable materials.

In some embodiments, dielectric materials, contact plugs, via plugs, metallic regions, and/or metallic lines (not shown) can be formed over the gate electrode portions for interconnection. The dielectric layers may include materials such as silicon oxide, silicon nitride, silicon oxynitride, low-k dielectric material, ultra low-k dielectric material, or any combinations thereof. The via plugs, metallic regions, and/or metallic lines can include materials such as tungsten, aluminum, copper, titanium, tantalum, titanium nitride, tantalum nitride, nickel silicide, cobalt silicide, other proper conductive materials, and/or combinations thereof. The via plugs, metallic regions, and/or metallic lines can be formed by any suitable processes, such as deposition, photolithography, etching processes, and/or combinations thereof.

In a first embodiment of this application, an integrated circuit includes a gate electrode disposed over a substrate. A source/drain (S/D) region is disposed adjacent to the gate electrode. The S/D region includes a diffusion barrier structure disposed in a recess of the substrate. The diffusion barrier structure includes a first portion and a second portion. The first portion is adjacent to the gate electrode. The second portion is distant from the gate electrode. An N-type doped silicon-containing structure is disposed over the diffusion barrier structure. The first portion of the diffusion barrier structure is configured to partially prevent N-type dopants of the N-type doped silicon-containing structure from diffusing into the substrate. The second portion of the diffusion barrier structure is configured to substantially completely prevent N-type dopants of the N-type doped silicon-containing structure from diffusing into the substrate.

In a second embodiment of this application, a method of forming an integrated circuit includes forming a gate electrode over a substrate. A recess is formed in the substrate and adjacent to the gate electrode. A diffusion barrier structure is formed in the recess. The diffusion barrier structure includes a first portion and a second portion. The first portion is adjacent to the gate electrode. The second portion is distant from the gate electrode. An N-type doped silicon-containing structure is formed over the diffusion barrier structure. The first portion of the diffusion barrier structure is configured to partially prevent N-type dopants of the N-type doped silicon-containing structure from diffusing into the substrate. The second portion of the diffusion barrier structure is configured to substantially completely prevent N-type dopants of the N-type doped silicon-containing structure from diffusing into the substrate. The N-type doped silicon-containing structure is thermally annealed.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. An integrated circuit comprising: a gate electrode disposed over a substrate; and a source/drain (S/D) region disposed adjacent to the gate electrode, the S/D region comprising: a diffusion barrier structure at least partially disposed in a recess of the substrate, wherein the diffusion barrier structure comprises an epitaxial layer, wherein the epitaxial layer comprises a first region and a second region, wherein the first region is thinner than the second region and is adjacent to the gate electrode, and the second region is distant from the gate electrode; and an N-type doped silicon-containing structure disposed over the diffusion barrier structure, wherein the first region of the diffusion barrier structure is configured to partially prevent N-type dopants of the N-type doped silicon-containing structure from diffusing into the substrate and the second region of the diffusion barrier structure is configured to substantially completely prevent N-type dopants of the N-type doped silicon-containing structure from diffusing into the substrate.
 2. The integrated circuit of claim 1, wherein the epitaxial layer comprises an epitaxial carbon-containing layer.
 3. The integrated circuit of claim 2, wherein the diffusion barrier structure further comprises a carbon implanted region between the epitaxial carbon-containing layer and the substrate.
 4. The integrated circuit of claim 2, wherein an interface between the first region and the substrate is directly under the gate electrode, and the interface is misaligned from a sidewall of the gate electrode by about 2 nm or less.
 5. The integrated circuit of claim 2, wherein an interface between the first region and the substrate is not directly under the gate electrode, and the interface is misaligned from a sidewall of the gate electrode by about 10 nm or less.
 6. The integrated circuit of claim 2, wherein the first region continuously extends from a surface of the substrate along a sidewall of the recess for about 7 nm or less.
 7. The integrated circuit of claim 6, wherein the first region has a substantially conformal thickness along the sidewall of the recess.
 8. The integrated circuit of claim 6, wherein a thickness of the first region gradually increases from the surface of the substrate along the sidewall of the recess.
 9. The integrated circuit of claim 1, wherein the N-type doped silicon-containing structure has a dopant concentration ranging from about 2E20 cm⁻³ to about 1E21 cm⁻³.
 10. A semiconductor device comprising: a gate structure over a substrate; and a source/drain (S/D) region disposed adjacent to the gate structure, the S/D region comprising: a diffusion barrier structure at least partially disposed in a recess of the substrate, wherein the diffusion barrier structure comprises an epitaxial layer, wherein the epitaxial layer comprises a first portion having a first thickness in a first direction parallel to a top surface of the substrate, a second portion having a second thickness in a second direction perpendicular to the first direction, and a third portion connecting the first portion to the second portion, wherein the first thickness is greater than the second thickness; and a doped silicon-containing structure disposed over the diffusion barrier structure.
 11. The semiconductor device of claim 10, the second portion extends to a depth of 7 nanometers (nm) or less below the gate structure.
 12. The semiconductor device of claim 10, wherein the second thickness varies from a top of the second portion closest to the gate structure to a bottom of the second portion distant from the gate structure.
 13. The semiconductor device of claim 10, wherein the S/D region further comprises a lightly doped drain (LDD) region between the second portion and the substrate.
 14. The semiconductor device of claim 13, wherein the S/D region further comprises a carbon implant region between the LDD region and the substrate.
 15. The semiconductor device of claim 14, wherein the carbon implant region comprises a carbon concentration ranging from about 0.1 atomic percent to about 1 atomic percent.
 16. The semiconductor device of claim 10, wherein the diffusion barrier structure comprises at least one of silicon carbide, silicon oxycarbide, silicon carbon nitride, or silicon carbon phosphorous.
 17. The semiconductor device of claim 10, wherein the first portion is a tapered structure comprising: a first segment substantially perpendicular to a top surface of the substrate and connected to the third portion, and a second segment connected to the first segment and the third portion, wherein the second segment is not perpendicular to the top surface of the substrate.
 18. A semiconductor device comprising: a gate structure over a substrate; and a source/drain (S/D) region disposed adjacent to the gate structure, the S/D region comprising: an epitaxial structure disposed in a recess of the substrate, wherein the epitaxial structure includes a first portion having a first thickness in a first direction parallel to a top surface of the substrate, a second portion having a second thickness in a second direction perpendicular to the first direction, and a third portion connecting the first portion to the second portion, wherein the first thickness is greater than the second thickness; a doped silicon-containing structure disposed over the epitaxial structure; and an implant region between the second portion and the substrate.
 19. The semiconductor device of claim 18, wherein the S/D region further comprises a lightly doped drain (LDD) region between the second portion and the implant region.
 20. The semiconductor device of claim 18, wherein the first portion is a tapered structure comprising: a first segment substantially perpendicular to a top surface of the substrate and connected to the third portion, and a second segment connected to the first segment and the third portion. 